SSH Notes

• MOTD = Message of the Day

• sudo vim /etc/issue.net Displays a message before the user begins login, I do not use this.
  • sudo vim /etc/ssh/sshd_config ensure the following option is set Banner /etc/issue.net (you can actually used any path/file)
  • sudo systemctl reload sshd needs to be performed after any change to the configuration file to activate the changes.
• sudo vim /etc/motd Displays the banner text after login. This usually has some predefined Linux distribution text

• ls -la /etc/update-motd.d/ to see the scripts that are run after the MOTD is displayed.

The Debian script is very simple:

#!/bin/sh
uname -snrvm

Ubuntu has multiple scripts some that I like and some that I do not like. This system status information script,

''/etc/update-motd.d/50-landscape-sysinfo'':

#!/bin/sh
# pam_motd does not carry the environment
[ -f /etc/default/locale ] && . /etc/default/locale
export LANG
cores=$(grep -c ^processor /proc/cpuinfo 2>/dev/null)
[ "$cores" -eq "0" ] && cores=1
threshold="${cores:-1}.0"
if [ $(echo "`cut -f1 -d ' ' /proc/loadavg` < $threshold" | bc) -eq 1 ]; then
    echo
    echo -n "  System information as of "
    /bin/date
    echo
    /usr/bin/landscape-sysinfo
else
    echo
    echo " System information disabled due to load higher than $threshold"
fi

The main information script is written in python3, /usr/bin/landscape-systeminfo:

#!/usr/bin/python3
import sys, os

try:
    if os.path.dirname(os.path.abspath(sys.argv[0])) == os.path.abspath("scripts"):
        sys.path.insert(0, "./")
    else:
        from landscape.lib.warning import hide_warnings
        hide_warnings()

    from twisted.internet import reactor

    from landscape.sysinfo.deployment import run
except ImportError:
    # For some reasons the libraries are not importable for now. We are
    # probably during an upgrade procedure, so let's exit, expecting the
    # dependencies to be fixed at next run.
    sys.exit(2)


if __name__ == "__main__":
    run(sys.argv[1:], reactor)

Some Links:

• https://www.simplified.guide/ssh/suppress-banner
• https://www.shellhacks.com/setup-warning-message-banner-ssh/
• https://www.tecmint.com/protect-ssh-logins-with-ssh-motd-banner-messages/